"It's not always the case, but the problem is when the Chinese are in the market you can't compete," Gesing said. "It's a totally economic choice, but it's a biased economic choice. If you were a shredder, why would you sort if you could sell the mixed material for more money than you could sell the products for in the North American market? The prices for sorted material by parent metal in North America and in Europe were less than what the Chinese and the Indians were paying for zorba." Zorba is the unsorted nonferrous goulash that gets past shredder magnets.

But China's hand-sort strategy might have begun losing some of its advantage. "While we are decreasing wages here to meet China, the Chinese wages are rising to meet ours," Gesing said. "Eventually the Chinese will replace the hand sorters on the docks in Guangzhou (the capital of China's southern coastal province of Guangdong) with particle sorters" that use sensor technologies.

Sensor sorting can work economically for U.S. scrap consumers willing to buy lower grades of material, Gesing said. However, the medium-term prospect is dim for such investments because of global restructuring.

"If the assembly plant is in China and the component manufacturing plants are being shifted to China, then the smelters are going to follow. The only people that will be left on our continent are the shredders," he said. "At that point it doesn't matter if the sorting plant is in Michigan or is sitting in Guangzhou, where all the scrap is arriving by container."

One issue is how far you need to sort before scrap goes into the melt. "You do need to sort by parent metal. And that's doable by hand, by the way it feels in the hand, by the color," Gesing said. "From aluminum, there is only one alloy you can make from old scrap—380 (for engine blocks). As long as there is enough market for your lowest common denominator alloy, anything more you're doing (to sort) is a waste."

The evolution of sensor technology has made heavy media separation obsolete, he said. Such technology uses fluids or aerated sand to segregate shredded materials by density.

The final breakthrough around 2005 was the X-ray sensor with dual energy levels, Gesing said. "With the advent of the sensor-based approach, I think it would be easier to operate a sensor-based system than a sand-based system."

Every shredder needs eddy-current sorting because the metal content is too low without it, according to Gesing. If the settings aim at a very high metal content, in the 90-percent range, the price is better. However, certain sorts of metals also have been eliminated by so high a target using eddy current.

"The further you're going to ship it, the more it makes sense to upgrade the scrap" by ratcheting up the ratio of metallics to nonmetallics in the eddy current's output, Gesing said, noting that recovering scrap prices are reviving the market for sensor sorting.

"It has probably changed enough that it actually makes sense to do it. The question is to whom does it make sense? To a shredder operator? At this point, probably not," he said. "It does make sense to the alloy producer in the aerospace industry—to make sure that production scrap can be refined back into aerospace alloys. That cannot be done by hand sorting. You're sorting by alloying elements."

He also sees room for expanded sensor sorting on the intake side of secondary smelters. "That's a way to get your hands on low-grade metal (from dealers and brokers) that they can upgrade and survive," he said.

A longtime observer from an adjacent industrial niche said several smelters have shaped their intake procedures around major quantities of media-flotation twitch. These are typically plants that supply molten alloy to the auto industry and favor scrap that doesn't need adjusting before melting. Those smelters are unlikely to abandon twitch, the source said.

But for most scrap consumers, "twitch in itself is constrained by the price of aluminum cast scrap. If I'm paying 70 cents (per pound) for old cast, I can't pay 80 cents for twitch. I've got to shred the cast and get out the 1- to 2-percent marginal iron. But crushed cast, metallurgically, can be a more desirable item than twitch," he said. "The Far East assesses the (shredded) product to remove all of the industrial metals from the car efficiently. We are still in that mindset of wanting to produce a steel product out of the car and an aluminum product out of the car."

Electronic scrap's unique problems can be dealt with by sensor technology, but the economics can be tricky, according to Gesing. "The problem with electronic scrap is that in order to liberate mono-material pieces you need to shred it finer. If you shred it finer to go to sensor sort, then your throughput goes down. The question then is the economics of doing a particular separation," he said. "If you have a fraction with precious metals, that makes all the sense in the world. And once you're doing a slow sort of finer particles, your sensors can spot and divert more effectively aluminum burdened with non-aluminum attachments."

So a slow sort, once chosen for the precious metals, can eliminate most aluminum contaminants. As for the contaminated aluminum stream, "you can reshred that portion to liberate those particles," Gesing added.

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